A new type of HIFU (High Intensity Focused Ultrasound) linear array transducer, which is able to simultaneously function as a therapy as well as imaging probe, will be developed during this program. Contradictory acoustic requirements for imaging and therapy result in disparate piezoelectric material characteristics for each mode of operation. To overcome this difficulty a hybrid transducer design is proposed that will decouple the transmission operation from the receive function yet maintain coplanar imaging and therapy. The transducer will combine the use of a piezoelectric ceramic for therapy and pulse generation with a separate integral PVDF copolymer transducer for image reception. The transmitter uses the superior electromechanical coupling coefficient of piezoceramic materials to improve efficiency and reduce thermal problems during high power generation. By configuring a separate PVDF receiver one is able to obtain greater sensitivity and bandwidth during image reception. The goal of this program is to demonstrate improved dual use transducer capability by: 1) Constructing a single element hybrid transducer to produce high intensity acoustic field while functioning as a high performance A mode transducer 2) Designing an active clamping circuit to produce short imaging pulses for pulse echo reception 3) Constructing an elemental phased array to measure adequate array performance for both therapy and imaging. In the longer term Spectrasonics will utilize this transducer design for the development and commercialization of ultrasonically guided HIFU therapy systems for the minimally- invasive treatment of diseases of the heart, vascular and abdominal organs such as the liver, kidney and pancreas. For its initial focus Spectrasonics has chosen cardiac ablation for the treatment of Atrial Fibrillation. Ultrasound therapy has been the subject of research for many years, but it is only recently that this technique has found effective and widespread medical applications. High Intensity Focused Ultrasound (HIFU) is a noninvasive technique capable of selective destruction of tissue volumes within the body. HIFU is designed to ablate tissue (produce lesions) in the focal region of an acoustic beam in a predictable and reproducible manner This technology represents a major advance in image guided, minimally invasive therapy, and offer the potential to provide significant improvements in the treatment for a wide variety of soft tissue diseases. [unreadable] [unreadable] [unreadable]